Is it permissible for an employee to benefit from the full amount deposited in the bank and operated with interest, which includes a deduction from his salary and an added percentage from UNRWA, knowing that this was done without his consent and he cannot receive it except upon termination of service?

The agency is not permitted to deduct anything from employees' salaries without their permission. If they grant permission, these funds may only be invested in permissible (halal (definition)) ventures, and it is not permissible to deposit them in banks that yield interest. The employee should look for another job, but if he is compelled (by necessity), there is no harm in continuing while still searching for an alternative. The funds received at the end of service include only what was deducted from his salary and what the agency granted him. He must donate the interest (the remainder) to charitable causes.